An image sensor is a sensor that detects and conveys image information by converting light into electrical signals. An active-pixel image sensor is a sensor in which each pixel has its own photodetector and an active amplifier.
One popular image sensor is the complementary metal-oxide-semiconductor (CMOS) sensor, which has overtaken other image sensor technology in many consumer applications due to its high noise immunity, low static power consumption and low cost.
In a typical CMOS image sensor, there is a 2D array of pixels, and each pixel includes a photodetector and an active amplifier. Light impacting upon each pixel causes electrical charges to accumulate on the pixels and an accumulated charge is read and transferred to signal processing circuitry. The accumulated charge may then be amplified by individual amplifiers at each pixel before being output as a voltage signal.